The enduring unpopularity of Windows 8 meant it was vital that Microsoft nail its next OS to prove that it was an aberration.

Windows 10, not Windows 9 as you and arithmetic would expect, looks to be a marked improvement.

Instead of adding a host of new complicated features, Windows 10 was designed to simplify - so much that it could work on screens ranging from 4 to 80 inches.

That’s the central conceit of Windows 10; creating a shared user interface for smartphones to tablets all the way up to PCs.

What are the key lessons from the launch of Windows 10?

Microsoft knows Windows 8 was a disaster

So keen was Microsoft to distance itself from the abomination of Windows 8 that they defied logic and skipped number 9. Their official explanation was vague: “This product, when you see the product in your fullness I think you'll agree with us that it's a more appropriate name.”

Everything else about Tuesday’s press conference was an admission that Windows 8 was a dud, and that the new OS will not be much like it.

Microsoft OS Chief Terry Myerson said: "It gives the familiarity of Windows 7 with some of the elements of Windows 8."

Touch is the main thing they’ll keep roughly the same, and the Charms bar will stay, though it will be fiddled with.

Microsoft pretty much came out and said that the user experience of Windows 8 was a lesson in what not to do.

Windows 10, on the other hand, will transition keyboard use with touch use, with the device’s interface changing depending on what the user has input.

The new Windows 10 Start Menu

Start menu makes a comeback

Windows 10 has put the Start Menu back at the front and left of the Microsoft user interface. When opened, the menu splits into two columns – one the traditional list, the other app-style icons.

Users can also manipulate the size and shape of the Start Menu and applications for which it is a doorway.

And there’s now universal search from the Start menu, including web results. All in all, it was a good day for Start.

Improved command prompt for computer geeks

Joe Belfiore, the man behind Windows Phone, confessed that this was a “geeky” function. Command prompt is not much used except by those who know what to do with it.

For those technology enthusiasts, command prompting got a whole lot easier with Windows 10. Whereas before you would have to open a context menu and hit paste, now you can use Ctrl+V as you do anywhere else.

Microsoft wants feedback

That’s what the Windows Insider Program is for. Myerson said: “We’re inviting our enthusiastic fans to evaluate [Windows 10] with us. We know they’re a vocal bunch.”

For those who know that “DLL is not the new OMG” or that “BIOS is not a plant-based fuel,” Microsoft is asking for your thoughts on the OS. Forums will be set up, as will discussions with Microsoft engineers.